Control apparatus for industrial trucks

Abstract

A control mechanism for the lift cylinder of an electric lift truck. A first pump motor is energized by the closing of a first switch in response to movement of the lift valve spool toward the lift position. A second pump motor is energized when the lift valve spool is in its full lift position and a bending moment is applied to the control rod controlling the lift valve spool of sufficient magnitude to elastically deflect the control rod into closing engagement with the switch.

We claim: 
     
       1. In a hydraulic system for an industrial truck load carriage comprising a hydraulic motor operatively connected to said load carriage; a first pump having an outlet connected to said hydraulic motor; a control valve connected between said first pump outlet and said hydraulic motor, said control valve including a valve spool movable between a first position permitting no oil flow from said first pump outlet to said hydraulic motor and a second position permitting maximum oil flow from said first pump outlet to said hydraulic motor; and a second pump having an outlet connected to said hydraulic motor in parallel with the outlet of said first pump; the improvement comprising control means for activating said second pump when said valve spool is in said second position, said control means comprising a control rod operatively connected to said valve spool and movable between a first position corresponding to the first position of said valve spool and a second position corresponding to the second position of said valve spool, and switching means operatively connected to said second pump and including an operating element movable in response to movement of said control rod to activate said second pump, said operating element being moved by said control rod only when a bending moment is applied to said control rod of sufficient magnitude to deflect said control rod a predetermined amount. 
     
     
       2. Apparatus as claimed in claim 1, in which said hydraulic motor comprises a hydraulic cylinder having a piston element connected to said load carriage. 
     
     
       3. Apparatus as claimed in claim 1, in which said control valve is connected between said second pump outlet and said hydraulic motor. 
     
     
       4. Apparatus as claimed in claims 1, 2 or 3, including an electric motor for driving said second pump, said switching means comprising a normally open electrical switch in circuit with said electric motor which is closed in response to movement of said control rod. 
     
     
       5. Apparatus as claimed in claims 1, 2 or 3 including a first electric motor for driving said first pump, first electric switch means responsive to movement of said valve spool from said first position toward said second position to close an electrical circuit to said first electric motor, and a second electric motor for driving said second pump, said switching means comprising a normally open electrical switch in circuit with said second electric motor which is closed in response to movement of said control rod. 
     
     
       6. Apparatus as claimed in claim 5 in which said control means comprises an elongated control rod having a handle formed at one end thereof, means formed at the opposite end of said control rod for engaging said valve spool, means mounting said control rod for rotation between said first position and said second position about a pivot axis perpendicular to the longitudinal axis of said valve spool, and means mounting said second electrical switch in a position to be closed by engagement with said control rod. 
     
     
       7. Apparatus as claimed in claim 6, in which said means mounting said control rod comprises a bracket mounted on said control valve, and said pivot axis is defined by a pin extending through said bracket and said control rod, said bending moment being applied about said pin.